Any auto parts store will have them for less than the dealer charges - I
think I paid about $1 for a three pack of them (I also have a Subaru). I
dunno if you can substitute a simple copper washer for the crush washer.
My Volvo and other cars I've owned use simple copper washers, they are
slightly cheaper. However, my Pontiac doesn't have any seal/gasket/washer
on the oil drain plug, and it doesn't leak - those clever American
engineers must know something that the Swedes, Germans and Japanese don't.

--
Ron DeBlock N2JSO
If God had meant for Man to see the sunrise,
He would have scheduled it later in the day.